As is indicated in Japanese Laid-open Patent Application No. 2001-201138, there is a known system including an air conditioner and a storage battery, in which, when a peak cut is requested from an electric power company that supplies electric power to the system, the air conditioner is operated by using the electric power of the storage battery charged during the night so as to ensure the comfort of the user of the air conditioner while complying with the request.
In such a system, keeping the storage battery always fully charged makes it easy to ensure the comfort of the user of the air conditioner while complying with the request for a peak cut.